left join on and和left join on wh

person表
infos表

sql1select person.name,infos.age from person LEFT JOIN infos on person.id = infos.person_id and infos.age=11

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sql2select person.name,infos.age from person LEFT JOIN infos on person.id = infos.person_id where infos.age=11

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left join on and这种写法会返回左表的所有数据
left join on where 会对数据进行筛选